US20230103803A1 - Process for recovering acrylic acid - Google Patents

Process for recovering acrylic acid Download PDF

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US20230103803A1
US20230103803A1 US17/801,806 US202117801806A US2023103803A1 US 20230103803 A1 US20230103803 A1 US 20230103803A1 US 202117801806 A US202117801806 A US 202117801806A US 2023103803 A1 US2023103803 A1 US 2023103803A1
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acrylic acid
solvent
stage
acid
stripping
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Ulrich Hammon
Klaus Joachim Mueller-Engel
Steffen Rissel
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BASF SE
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D11/00—Solvent extraction
    • B01D11/04—Solvent extraction of solutions which are liquid
    • B01D11/0492—Applications, solvents used
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D11/00—Solvent extraction
    • B01D11/04—Solvent extraction of solutions which are liquid
    • B01D11/0488—Flow sheets
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/14—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by absorption
    • B01D53/1431—Pretreatment by other processes
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/14—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by absorption
    • B01D53/1487—Removing organic compounds
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/14—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by absorption
    • B01D53/1493—Selection of liquid materials for use as absorbents
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C51/00—Preparation of carboxylic acids or their salts, halides or anhydrides
    • C07C51/16—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation
    • C07C51/21—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation with molecular oxygen
    • C07C51/25—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation with molecular oxygen of unsaturated compounds containing no six-membered aromatic ring
    • C07C51/252—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation with molecular oxygen of unsaturated compounds containing no six-membered aromatic ring of propene, butenes, acrolein or methacrolein
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C51/00—Preparation of carboxylic acids or their salts, halides or anhydrides
    • C07C51/42—Separation; Purification; Stabilisation; Use of additives
    • C07C51/43—Separation; Purification; Stabilisation; Use of additives by change of the physical state, e.g. crystallisation
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C51/00—Preparation of carboxylic acids or their salts, halides or anhydrides
    • C07C51/42—Separation; Purification; Stabilisation; Use of additives
    • C07C51/43—Separation; Purification; Stabilisation; Use of additives by change of the physical state, e.g. crystallisation
    • C07C51/44—Separation; Purification; Stabilisation; Use of additives by change of the physical state, e.g. crystallisation by distillation
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C51/00—Preparation of carboxylic acids or their salts, halides or anhydrides
    • C07C51/42—Separation; Purification; Stabilisation; Use of additives
    • C07C51/47—Separation; Purification; Stabilisation; Use of additives by solid-liquid treatment; by chemisorption
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C51/00—Preparation of carboxylic acids or their salts, halides or anhydrides
    • C07C51/42—Separation; Purification; Stabilisation; Use of additives
    • C07C51/48—Separation; Purification; Stabilisation; Use of additives by liquid-liquid treatment
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D11/00—Solvent extraction
    • B01D11/04—Solvent extraction of solutions which are liquid
    • B01D11/0426—Counter-current multistage extraction towers in a vertical or sloping position
    • B01D11/043—Counter-current multistage extraction towers in a vertical or sloping position with stationary contacting elements, sieve plates or loose contacting elements
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2252/00—Absorbents, i.e. solvents and liquid materials for gas absorption
    • B01D2252/20—Organic absorbents
    • B01D2252/205—Other organic compounds not covered by B01D2252/00 - B01D2252/20494

Definitions

  • the present invention relates to a process for recovering acrylic acid which is obtained by catalytic gas phase oxidation of propene.
  • acrylic acid is a valuable monomer and intermediate for production of polymers that are used for a wide variety of different products, for example absorbent resins, binders for aqueous emulsion paints and the like.
  • Acrylic acid is produced on a large scale by a heterogeneously catalyzed partial gas phase oxidation of propene and/or acrolein with oxygen or oxygen-comprising gases in the presence of solid catalysts and at elevated temperature.
  • the heterogeneously catalyzed partial oxidation of propene to acrylic acid is especially undertaken in two successive steps, wherein the first reaction step converts the propene to acrolein and the second reaction step the acrolein to acrylic acid, which is frequently conducted in two spatially separate reaction stages.
  • Some of these secondary components are of higher volatility than acrylic acid (for example acetic acid) and are also referred to as “low boilers”. Others are of lower volatility than acrylic acid (for example phthalic anhydride) and are accordingly referred to as “high boilers”. “Medium boilers” refer to secondary components having similar volatility to acrylic acid.
  • the basic removal of the acrylic acid from the gaseous product gas mixture is generally effected by sorption methods, for example by countercurrent absorption of the acrylic acid with a first solvent or solvent mixture.
  • the solvent used is water, which scrubs the acrylic acid out of the gas stream after the synthesis.
  • the further removal of the water is effected by an extraction and subsequent distillation steps.
  • azeotrope method In a second process variant (which can also be referred to as “azeotrope method”), the absorption is likewise followed by washing with water, and the removal of water is conducted by an entraining agent distillation (azeotropic distillation) and further distillation steps.
  • a further process variant (which can also be referred to as “crystallization method”) involves fractionally condensing the reaction gas without adding a first solvent, with further workup by crystallization.
  • the acrylic acid is absorbed from the gas stream with a high-boiling hydrophobic first solvent. This absorption of acrylic acid is selective, meaning that the water vapor present in the gas stream from the synthesis remains largely in the gas phase.
  • the fourth process variant is described, for example, in WO 2011/000808 A2 in the form of a process for separation of acrylic acid, specifically a process for separation of acrylic acid from a product mixture from a heterogeneously catalyzed partial gas phase oxidation of at least one C3 precursor compound to give acrylic acid, which comprises not only acrylic acid, water vapor and glyoxal but also low boilers excluding the aforementioned compounds, medium boilers, high boilers and components that are difficult to condense as secondary constituents.
  • the product gas mixture is cooled in a direct cooler by direct cooling with a finely sprayed cooling liquid, with evaporation of a portion of the cooling liquid.
  • the cooled product gas mixture together with evaporated and unevaporated cooling liquid is guided into the bottom space of an absorption column which is connected to the absorption space of the absorption column above that has separating internals via a chimney tray KB 1 present between the two that has at least one chimney, and from which the cooled product gas mixture and evaporated cooling liquid flow through the at least one chimney of the chimney tray KB 1 into the absorption space and ascend therein in countercurrent to a high-boiling (first) absorbent descending therein.
  • absorbate A comprising acrylic acid absorbed in absorbent accumulates on the chimney tray KB 1 . From the chimney tray KB 1 , absorbate
  • A comprising acrylic acid absorbed in absorbent that accumulates thereon is conducted out of the absorption column, a portion of absorbate A conducted out of the absorption column is fed to the bottom space of the absorption column to form a bottoms liquid present in the bottom space, and another portion of the absorbate A is optionally cooled and recycled into the absorption column above the chimney tray KB 1 .
  • Low boilers are optionally stripped out of the remaining residual amount RA of absorbate A conducted out of the absorption column in a stripping unit to produce an absorbate A* depleted of low boilers.
  • the residual amount RA of absorbate A or the absorbate A* is fed to a rectification column having a rectifying section and stripping section, the absorbent is enriched in the stripping section of the rectification column and absorbent with a proportion by weight of acrylic acid ⁇ 1% by weight is conducted out of the stripping section, the acrylic acid is enriched in the rectifying section of the rectification column, and a crude acrylic acid P having a proportion by weight of acrylic acid >90% by weight is conducted out of the rectifying section.
  • Absorbent-comprising bottoms liquid is withdrawn from the bottom space of the absorption column, a portion of this withdrawn bottoms liquid is fed as cooling liquid to the direct cooler, and the residual amount of this withdrawn bottoms liquid is sent to a distillation unit comprising a distillation column and a circulation heat exchanger, the bottoms liquid fed to the distillation unit is separated by distillation in the distillation column into vapors wherein the proportion by weight of absorbent is greater than the proportion by weight of absorbent in the bottoms liquid, and into liquid concentrate wherein the proportion by weight of constituents B that are higher-boiling than the absorbent is greater than the proportion by weight of constituents B in the bottoms liquid.
  • a partial volume flow rate TAu of this volume flow rate M from the process of removing acrylic acid is discharged from the product mixture, and the residual stream RM of the volume flow rate M is returned to the distillation column above the withdrawal of the volume flow rate M from the distillation column with temperature T2>T1 via the circulation heat exchanger.
  • the average dwell time tv of the constituents of the partial volume flow rate TAu in the distillation unit is ⁇ 40 h.
  • the third process variant is disclosed, for example, in DE 103 32 758 A1 or WO 2015/091628 A1.
  • the reaction gas as in the fourth process variant, is cooled down by injecting and subsequent evaporation of a cooling liquid and then guided into a condensation column comprising separating internals.
  • the acrylic acid is absorbed by the reflux from the absorption column, still with enrichment of low-boiling and high-boiling compounds at the top and in the bottom region of the condensation column.
  • a more than 90% by weight present acrylic acid is guided into a downstream crystallization system for further purification.
  • the acrylic acid product is drawn off from the crystallization plant in a purity of >99% by weight.
  • the impurities removed in the crystallization plant are recycled as “mother liquor” into the condensation column for further processing.
  • a high boiler fraction is drawn off, which is transferred into a cleavage column, where oligomeric acrylic acid is cleaved into monomeric acrylic acid, and the acrylic acid removed is recycled in gaseous form into the condensation column.
  • the high boiler residue is drawn off in liquid form from the bottom of the cleavage column and sent to a disposal unit.
  • the gas exiting from the separating region of the absorption column is cooled in a condensation section, wherein condensable secondary components, essentially water of reaction and acetic acid and unremoved acrylic acid, are condensed out.
  • the “acid water” thus obtained is transferred into a disposal unit at the top of the column via an extraction unit. In the extraction unit, the acrylic acid present in the acid water is removed and recycled into the absorption column.
  • a disadvantage of the workup in the fourth process variant, especially with respect to the third process variant, is distinctly elevated loss of valuable acrylic acid product, which has to date been extracted only inadequately from the acid water.
  • the objective technical problem addressed by the present invention is therefore that of specifying a process for recovering acrylic acid and of providing a corresponding plant with which the proportion of acrylic acid remaining in the acid water can be distinctly reduced, in order thus to improve the overall yield in acrylic acid production, especially with employment of the workup according to the fourth process variant.
  • This object is achieved in the first aspect of the present invention by a process for recovering acrylic acid which is obtained by catalytic gas phase oxidation of propene, wherein, in an absorption stage (K 2 ), the acrylic acid is absorbed from the reaction mixture ( 1 ) from the gas phase oxidation with a first solvent ( 3 ) and is drawn off for distillative purification, and a gas mixture from the absorption stage (K 2 ) is passed onward to a condensation stage,
  • an acid water stream ( 4 or 4 *) is obtained in the fourth process variant, which, as well as the low-boiling condensable secondary components as in the third process variant, also obtain high-boiling secondary components, diacrylic acid and residues of solvent constituents. It was therefore considered unviable and unfeasible to date to apply an additional extraction of the acid water as conducted in the third process variant to the fourth process variant.
  • the process of the invention therefore has the advantage that the provision of an additional acid water extraction with subsequent solvent treatment can distinctly reduce the proportion of acrylic acid present in acid water which is sent to disposal. More particularly, it is possible to reduce the proportion of acrylic acid to below 1% by weight, based on the total weight of the wastewater stream ( 11 ). This can simultaneously improve the overall yield of acrylic acid, based on the overall process of the fourth process variant, by up to 2%.
  • the extraction stage (K 7 ) is preceded by a preliminary extraction stage in which a substream ( 12 ) of the first solvent stream exiting from the stripping cycle gas scrubber (K 5 ) is fed into the acid water ( 4 ), the phases are separated in the phase separation vessel (B 1 ) and then the first solvent ( 3 ) separated off is fed to the absorption stage (K 2 ), and the acid water ( 4 *) separated off in the phase separation vessel (B 1 ), after preliminary extraction in the preliminary extraction stage, is introduced into the extraction column (K 7 ).
  • the preliminary extraction upstream of the extraction stage (K 7 ), as well as removing the solvent from the acid water ( 4 ), can especially significantly reduce the proportion of diacrylic acid in the first solvent stream ( 10 ), especially to a value below 1.5%, based on the total weight of the first solvent stream ( 10 ).
  • This dimeric acrylic acid is taken up in the acid water stream ( 4 ) and sent to the extraction stage (K 7 ).
  • the absorption stage (K 2 ) is operated with a feed temperature of 45° C. to 65° C. and a drain temperature of 100° C. to 125° C., as a result of which the acid water ( 4 ) drawn off from the condensation stage also comprises diacrylic acid as well as an elevated content of acrylic acid.
  • the increase in temperature prevents the formation or entrainment of glyoxal, which is a polymerization-promoting component that lowers the purity of the acrylic acid.
  • glyoxal is a polymerization-promoting component that lowers the purity of the acrylic acid.
  • the advantage of the smaller amount of glyoxal results in a higher proportion of acrylic acid in the acid water and increased formation of diacrylic acid.
  • the absorption stage (K 2 ) can be operated at higher temperature.
  • the effect of the elevated temperature is more effective removal of low-boiling secondary components, which improves the fouling characteristics in downstream heat exchangers and separation apparatus and the product quality.
  • the mode of operation at elevated temperature in the absorption stage (K 2 ) of the fourth process variant increases plant availability because downstream plant components are soiled less quickly and hence longer cycles can be run without shutdown for cleaning.
  • there is a drop in energy consumption because fewer low-boiling components have to be removed in the separating operations downstream of the absorption in order to achieve the target quality of the product.
  • there is also a rise in the proportion of acrylic acid and diacrylic acid in the acid water In addition to the longer period of operation, the result is thus a higher recovery potential for acrylic acid from the acid water.
  • the diacrylic acid is selectively extracted as well as the acrylic acid, split in the stripping column (K 8 ) in step b), and in this way obtained as monomeric acrylic acid.
  • the stripping cycle gas scrubber (K 5 ), in the flow of the first solvent ( 3 ), is preceded by a cooling device (W 1 ) with which the first solvent ( 3 ) is precooled, in order to compensate for the elevated energy input as a result of the introduction of the stripping cycle gas from the stripping column (K 8 ) of the acid water extraction.
  • the higher temperature of the gas stream fed to the stripping cycle gas scrubber (K 5 ) would significantly increase the temperature conditions in this column and hence greatly reduce the intended scrubbing effect on the cycle gas in the column.
  • the provision of the cooling device (W 1 ) can keep the temperature in the stripping cycle gas column (K 5 ) at the desirably low level of 30° C. to 50° C. and hence establish the desired scrubbing effect without losses.
  • the first solvent comprises a mixture of Diphyl and dimethyl phthalate, and the second solvent dimethyl phthalate or diethyl phthalate.
  • Diphyl is understood to mean a diphenyl oxide/diphenyl eutectic in a ratio of 3:1.
  • a mixture comprising Diphyl and dimethyl phthalate has been found to be useful as first solvent with regard to absorption capacity for acrylic acid with simultaneously low fouling characteristics in the absorption.
  • Dimethyl phthalate and diethyl phthalate are notable for a high selective extraction capacity for acrylic acid in a substance mixture of water and other organic acids, for example formic acid and acetic acid, and diethyl phthalate is particularly suitable since it has a very low solubility in the raffinate after extraction coupled with high selectivity for acrylic acid alongside lower carboxylic acids such as acetic acid and formic acid.
  • a plant for recovery of acrylic acid having an absorption stage (K 2 ) for absorption of acrylic acid from the reaction mixture from a gas phase oxidation and a subsequent condensation stage for condensation of the gas mixture as acid water ( 4 ), further comprising
  • the plant of the invention is more particularly designed to conduct the above-described process of the invention.
  • the plant of the invention in principle has the same advantages as the process of the invention, namely that the provision of an additional acid water extraction (extraction stage (K 7 )) with subsequent solvent treatment (stripping column (K 8 )) can distinctly reduce the proportion of acrylic acid present in acid water which is sent to disposal.
  • this further comprises a preliminary extraction stage disposed upstream of the extraction stage (K 7 ) in the acid water conduit.
  • the provision of the preliminary extraction of the invention enables not only the removal of solvent from the acid water but more particularly a significant increase in the proportion of diacrylic acid in the stream of the first solvent ( 3 ).
  • the plant also comprises a cooling device (W 1 ) for precooling of the first solvent stream ( 10 ), wherein the cooling device (W 1 ) is disposed upstream of the stripping cycle gas scrubber (K 5 ).
  • the provision of the cooling device (W 1 ) can distinctly reduce any adverse effect of the stripping cycle gas scrubber (K 5 ) as a result of the higher temperature of the gas stream supplied.
  • a heat exchanger (W 4 ) for cooling the extractant stream before entry into the extraction column (K 7 ) is provided in the plant of the invention.
  • This heat exchanger (W 4 ) serves to limit the losses of the second solvent via the raffinate.
  • FIG. 1 a schematic diagram of the inventive part of a plant for recovery of acrylic acid
  • FIG. 2 a flow diagram of the inventive part of the plant shown in FIG. 1 and
  • FIG. 3 a diagram showing the influence of the absorption temperature on the losses of acrylic acid.
  • Both technical and economic factors affect the economic viability of the recovery of acrylic acid.
  • the technical factors include the fact that raising of the temperature in the absorption stage K 2 extends the service life of the plant, but simultaneously also increases the acrylic acid concentration in the acid water.
  • the economic factors especially include the rise in the price of propene in recent years by 40%.
  • the acid water in the present case comprises about 2.5% of the total acrylic acid production and, according to prior art, goes directly to incineration. Since the economic incentive is now quite high, the economic potential at a conservative estimate being €2 to €4 million per annum and plant, the present invention brings enormous benefits.
  • FIG. 1 shows a schematic of the basic principle of the relevant part of a plant of the invention for performance of the process of the invention.
  • Acid water from absorption and condensation i.e. from the absorption stage K 2 and the condensation stage, is first sent to the preliminary extraction stage and then routed into the extraction stage K 7 .
  • the first Diphyl solvent is removed and sent back to the absorption stage K 2 .
  • the second dimethyl phthalate solvent comprising the acrylic acid is removed from the acid water and circulated via the stripping column K 8 to the extraction stage K 7 .
  • the acrylic acid removed in the stripping column K 8 is fed to the stripping cycle gas scrubber K 5 .
  • FIG. 2 shows a flow diagram of the inventive part of the plant of the invention shown in FIG. 1 , which corresponds in terms of its basic structure to a plant of the fourth process variant, but according to the invention has an acid water extraction in the extraction stage K 7 with subsequent solvent recovery and acrylic acid removal in the stripping column K 8 .
  • the extraction column K 7 preferably has a structured packing as separating internals and more preferably a packing divided into individual segments by plates (as described in WO 2015/091628 A1).
  • the stripping column K 8 is equipped with plates (dual-flow, Thormann, sieve or bubble-cap trays).
  • the bottoms heat exchanger W 3 used in the stripping column K 8 is preferably a forced circulation flash evaporator.
  • FIG. 3 shows how the acrylic acid losses rise with rising temperature in the solvent feed, and how far these losses can be reduced by means of extraction.
  • Solvents shown here in comparison are diethyl phthalate (DEP) and dimethyl phthalate (DMP), particular preference being given to dimethyl phthalate since it is already a fixed constituent of the first solvent.
  • DEP diethyl phthalate
  • DMP dimethyl phthalate
  • One advantage of the process conditions of the workup by the third process variant is that virtually no diacrylic acid is present in the acid water output from the condensation column.
  • a significant amount of diacrylic acid is formed, or goes through the preliminary extraction into the acid water 4 drawn off from the absorption stage K 2 . Since this water is sent directly to a thermal disposal, this proportion of diacrylic acid in the acid water 4 constitutes a direct loss of acrylic acid.
  • the aim of this preliminary extraction was to separate the medium-boiling and high-boiling secondary components from the first solvent, not to recover acrylic acid.
  • the anhydrides of phthalic acid and maleic acid were removed here.
  • a portion of the solvent was run in each case through the preliminary extraction.
  • diacrylic acid there are small proportions (0.5% by weight-1.5% by weight) of diacrylic acid, which is largely transferred to the acid water by the preliminary extraction.
  • this not inconsiderable proportion of dimerized product too was withdrawn from the process and discarded as waste.
  • the aim of the present invention was to increase the economic viability of the fourth process variant for workup even in the case of elevated feed temperatures of the first solvent to the absorber.
  • Elevated feed temperatures here mean temperatures >50° C.
  • the acid water stream 4 * is supplied at the base and contacted with the stream of the second solvent 5 , preferably dimethyl phthalate (DMP), in a countercurrent extraction.
  • the dimethyl phthalate here absorbs the acrylic acid (and diacrylic acid) in high selectivity and is withdrawn from the extraction stage K 7 as stream 6 .
  • the raffinate 11 is removed, which consists essentially of water and comprises small amounts of acetic acid, formic acid, phthalic acid and maleic acid. This is sent to disposal.
  • the acrylic acid-laden extract/second dimethyl phthalate solvent after the stripping column K 8 of the invention has been heated, is applied at the top, and the acrylic acid is stripped out with the cycle gas 8 .
  • the heat required for the stripping is fed in at the bottom via a solvent circuit via a bottoms heat exchanger W 3 .
  • the breakdown of the diacrylic acid increases the total amount of acrylic acid recycled in accordance with the invention.
  • the total amount of the stripping gas or cycle gas is therefore greater than in the corresponding columns for the third process variant, which has an effect on the geometric design of the stripping column K 8 of the invention.
  • Acrylic acid- and diacrylic acid-depleted second dimethyl phthalate solvent is withdrawn from the bottom of the stripping column K 8 , while the cycle gas 9 with a significant amount of acrylic acid is drawn off at the top of the stripping column K 8 .
  • the cycle gas stream 9 laden with the recycled acrylic acid from the stripping column K 8 is fed to the stripping cycle gas scrubber K 5 .
  • the gas loading of this column remains virtually unchanged compared to operation without the acid water extraction of the invention.
  • the basis used for the design of the plant was the design of the stripping column as used in the third process variant.
  • This now inventive stripping column K 8 was designed with nine equilibrium stages and a bottoms specification, i.e. of the purity of solvent recycled, of 1385 ppm of acrylic acid.
  • the cycle gas stream through the stripping column K 8 was increased until the acrylic acid concentration at the top of the stripping column K 8 in the cycle gas recycled into the process was as high as in the third process variant, i.e. about 5% by weight.
  • a similar concentration profile in the stripping column K 8 to that in the third process variant surprisingly arises, such that the design can be implemented with low risk on the basis of the existing columns.
  • the risk in respect of the operation of the plant for the process of the invention is relatively low since the entire acid water extraction of the invention can be circumvented in a bypass, and hence the state prior to the alteration in accordance with the invention can be restored at any time.
  • acrylic acid 11.6% by weight water 5.0% by weight O 2 , N 2 , CO, CO 2 82.3% by weight propene, propane, acrolein 0.4% by weight acetic acid 0.3% by weight other carboxylic acids and aldehydes 0.4% by weight
  • an absorption stage K 2 the gas was subjected to a countercurrent absorption in which 138 t/h of a solvent mixture (first solvent 3 ) at a temperature of 59° C. and with a composition of
  • phase separator B 1 which was fed to a phase separator B 1 .
  • 16.2 t/h of first solvent that was taken from the bottom of the stripping cycle gas scrubber K 5 was mixed into the acid water 4 for preliminary extraction.
  • the solvent separated out in the phase separation vessel B 1 after preliminary extraction, was routed into the absorption section of the absorption stage K 2 at a volume flow rate of 18.3 t/h.
  • a mixture of first solvent with acrylic acid was drawn off from the absorption section of the absorption stage K 2 at a temperature of 114° C. and with a composition of
  • the acrylic acid-laden first solvent stream 10 was subjected to a vacuum distillation, and the product drawn off was 30 t/h of acrylic acid with a purity of 99.7% by weight at the side draw from the purifying column.
  • the acid water extraction column K 7 had a diameter of 0.9 m and was packed over a length of 34 m with a Montz B1-350 structured packing.
  • the packing was divided into four circular segments of equal size over the entire length by means of vertical plates in a crossed arrangement.
  • the volume of the upper and lower phase separation regions was 3 m 3 .
  • a second solvent 5 that consisted essentially of dimethyl phthalate was introduced at the top of the extraction column K 7 in an amount of 15 t/h at a temperature of 55° C., where it was distributed uniformly over the cross section of the column K 7 .
  • This acid water was fed into a plant for thermal treatment. Since there was still a residual content of acrylic acid and diacrylic acid in the raffinate stream 11 fed to the disposal unit, the loss of product of value was 108 kg/h or 0.36% based on the production of 30 t/h.
  • the extract After phase separation at the base of the extraction column K 7 , the extract, in an amount of 18 t/h and with a composition of
  • the stripping column K 8 had a length of 16.3 m and had an internal diameter that was uniform over the length of 2.6 m.
  • the column K 8 was equipped with 5 dual-flow trays in the lower section and with 15 valve trays in the upper section.
  • the tray separation in the region of the dual-flow trays was 600 mm, and in the valve tray region 500 mm.
  • the bottoms region of column K 8 had a capacity of 14 m 3 to accommodate the bottom product.
  • the stripping gas was run in an amount of 30 t/h at a temperature of 130° C. into the bottom of the stripping column K 8 , and corresponded in terms of this composition after compression in a cycle gas compressor to the gas that was obtained at the top of the absorption stage K 2 .
  • the bottom product from the stripping column K 8 was heated to 190° C. by means of a steam-heated shell-and-tube heat exchanger and circulated via the tray 5 .
  • the liquid volume of the pipeline system together with the heat exchanger through which the liquid was circulated was 2.5 m 3 .
  • the acrylic acid- and diacrylic acid-depleted bottom product from column K 8 after indirect heat exchange in heat exchangers W 2 and W 4 , was cooled down to 55° C. and introduced back to the top of the extraction column K 7 .
  • the second solvent entering the extraction column K 7 had the following composition:

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  • Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
US17/801,806 2020-02-25 2021-02-09 Process for recovering acrylic acid Pending US20230103803A1 (en)

Applications Claiming Priority (3)

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EP20159363.9A EP3733637A1 (de) 2020-02-25 2020-02-25 Verfahren zur rückgewinnung von acrylsäure
EP20159363.9 2020-02-25
PCT/EP2021/053090 WO2021170397A1 (de) 2020-02-25 2021-02-09 Verfahren zur rückgewinnung von acrylsäure

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WO2011000808A2 (de) 2009-07-01 2011-01-06 Basf Se Verfahren der abtrennung von acrylsäure aus dem produktgasgemisch einer heterogen katalysierten partiellen gasphasenoxidation wenigstens einer c3-vorläuferverbindung
DE102013226428A1 (de) 2013-12-18 2015-06-18 Basf Se Extraktionskolonne und Verfahren zum Extrahieren eines Bestandteils aus einem Fluid
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